Unit Does Not Ignite When Water Goes Through It; Abnormal Sounds Come From The Unit - A.O. Smith ATI-140H-N Service Handbook

plate. If the maximum
energy input of all appliances
exceeds the maximum rating
of the gas meter, consult
your local gas utility.
◦
For LP models, there may
not be enough gas left in the
propane tank.
◦
Verify that the supply
gas pressure is within
specification, not only when
the heater is in standby,
but also while the heater is
running on maximum fire.
(See "Checking Inlet Gas
Pressure/Purging Air from
Gas Line" on page 25.)
◦
The gas supply pressure
may be too low. This may be
caused by a malfunctioning
gas supply regulator.
◦
Check the pressure difference
between static and maximum
operating pressure. If the
drop is more than 1 inch W.C.,
there may be insufficient gas
supply. NOTE: In Canada, do
not exceed the maximum
allowable pressure drop
permitted by B149.1.
•
Venting:
◦
Verify that the venting is
installed to manufacturer's
specifications.
◦
Verify that the vent run
does not exceed the
allowable limit. Refer to
the installation manual.
◦
Verify that the DIP switch
settings for vent length
match the installation's
equivalent vent length and
diameter.
•
The filter on the cold water inlet
should be clean. Look for signs of hard
water scaling. See "Unit Draining and
Filter Cleaning" (p. 24).
•
If the clear tube from the
proportional gas valve to the
bottom of the combustion
chamber is disconnected,
fluctuations in temperature and/
or very low flow to the fixtures
may occur.
•
On well systems or even on
some city water systems, water
pressure fluctuations (especially
on low flow) of 8 to 10 psi will
result in flow rate fluctuations.
This may result in minor
temperature fluctuations.
•
Flow sensor or water control
valve may be compromised.
Inspect both parts for blockages
or debris.
Unit does not ignite when
water goes through it.
•
If you use the remote controller,
is the remote power button
turned on?
•
Check to see if the Computer
board is receiving power. This
can be verified by observing
the green LED on the computer
board or the amber LED on the
temperature/remote controller.
If it is not lit, the computer board
is not being powered. Check to
see if the ON/OFF switch below
the fuse box is set to the on
position, or if the fuse in the fuse
box assembly is blown.
•
Is the flow rate over 0.5 gpm?
See if the unit initiates when you
increase demand of water being
drawn through the unit (e.g.,
opening up more hot fixtures).
You can verify the flow rate by
pressing the info button on the
front of the unit until the arrow
lights up beside "flow."
Condensing Models: On-Demand Water Heater Service Handbook • 9
•
If the unit is in a recirculation
system, the return water
temperature may be too close
to the set point temperature
to activate the water heater.
You can verify the incoming
water temperature by using the
information button on the front
of the unit.
•
Check that the gas line is open
and is purged of air (page 25).
•
Check that the filter on the cold
water inlet is clean (page 24).
•
Check for a reversed connection of
the plumbing to the water heater
or a crossed connection in the
plumbing system. See page 25.
•
Check for problems with the
recirculation system.
Make sure that a check valve
is installed between the pump
discharge and the connection
to the cold water supply. A
malfunctioning or missing
check valve will cause a cross
connection, allowing cold water
to back-feed into the system.
•
If the fan does not initiate at
all and it is verified that there
is power to the unit, the flow
sensor may not be working
properly. Check the flow sensor
for proper impeller functionality.
Abnormal sounds come from
the unit.
•
Check the fan for debris.
◦
Check for blockages in the
exhaust vent and intake air
line.
◦
Check for proper gas supply
pressure.
•
Contact the technical service
department.